(1) Field of the Invention
The present invention relates to an image reading apparatus for reading original documents, which is applied to facsimile machines, copiers, scanners, printers etc.
(2) Description of the Prior Art
In conventional image reading apparatus for reading original documents for facsimile machines etc., an original is read using CCD image sensors or the like whilst it is being moved by a feed motor etc., and the thus picked up image information of the original is stored into the image memory incorporated in the facsimile machine. The stored image information will be sent out onto phone networks through a modem, if the machine is used as a facsimile.
The transmission rate of the image information sent out onto the phone network varies depending upon the capacity of the opposite facsimile machine or the status of the phone network. For example, in some cases such as when a large quantity of original documents need to be picked up, or when the transmission rate to the network is slower than the speed of reading original, the amount of data in the image memory may become its maximum. FIG. 1 shows the change in the amount of data in the image memory depending upon time. In this figure, the data in the image memory has become its maximum at time T0.
If the amount of data in the image memory reaches its maximum, no more data can be stored therein. Therefore, the operation of original reading must be stopped temporarily. The operation of reading the original will be restarted only after some image information has been sent out onto the phone network and thereby some empty areas have been secured inside the image memory.
However, if the operation of original reading is halted, the feed motor for conveying the original must be stopped. If this stoppage is done abruptly, the quality of the image may be degraded: the CCD image sensor picks up the same area repeatedly, whereby the printout on the receiver side facsimile machine will have a transverse line etc., which bears no relation to the original content. Further, there occurs a case in which if the feed motor is stopped abruptly, the motor cannot stop instantly but continues to rotate to some degree until it stops completely. This transient phenomenon may degrade positional accuracy of reading with respect to the original's direction of movement.
These drawbacks can be eliminated if a high capacity image memory is used in order not to disrupt the operation of original reading. But, a high capacity memory costs more.
The above problems also occur in other types of facsimile machines having a compressing function, or in scanners for transmitting the scanned image information to the host computer. Illustratively, in a facsimile machine having a compressing function, the picked up image information is sent to its compressing circuit through a buffer memory. In this case, if the speed of compression of the image information is lower than that of reading the original, the amount of data in the buffer memory may become its maximum in some cases. Therefore, the feed motor must be stopped abruptly in order to temporarily disrupt the operation of reading the original.
Further, in a scanner, when the image information scanned is sent to the host computer, the image information will be stored into the image memory in a similar manner to the facsimile machine. Also in this case, if the transmission rate of the image information to the host computer is lower than that of scanning the original, the amount of data in the image memory reaches its maximum, thus giving rise to a similar problem.
An image reading apparatus for dealing with these problems has been disclosed in Japanese Patent Application Laid-Open Hei 7 No. 264,358. In accordance with the image reading apparatus defined in this disclosure, when the original reading is disrupted, the feed motor is stopped abruptly, and the feed motor is reversed so that the correct position of reading is restored, taking into consideration the transient movement of the feed motor, thereafter original reading is restarted. Accordingly, it is possible to avoid the problem originating from the transient movement occurring when the feed motor is stopped, however the feed motor must be reversed so that it needs additional wasted time for reading the original.